This invention relates to a rotary hammer, and particularly relates to a rotary hammer with a mode change mechanism for switching the rotary hammer for operation in any one of a hammer only mode, a rotary drive only mode and a rotary hammering mode.
In a hammer only mode of a conventional rotary hammer, a bit is inserted into a tool holder of the hammer and is repeatedly struck by a hammering mechanism and is not rotatably driven. In a rotary drive only mode, the bit is rotatably driven and is not subject to impacts from the hammering mechanism. In a rotary hammering mode, the bit is repeatedly struck by the hammering mechanism and is simultaneously rotatably driven.
Conventional rotary hammers of this type typically include a spindle mounted for rotation within a housing of the hammer which can be driven by a rotary drive arrangement, selectively engageable and disengageable with a pinion driven by a motor of the hammer. The spindle rotatably drives a tool holder of the hammer which in turn rotatably drives a tool or bit releasably secured within the hammer. A piston is generally slideably located within the spindle and is reciprocally driven by a hammer drive mechanism which translates the rotary drive of a hammer motor to a reciprocating drive of the piston. A ram, also slideably located within the spindle, forward of the piston, follows the reciprocation of the piston due to successive reversing pressures in an air cushion within the spindle between the piston and the ram. The ram repeatedly impacts an anvil slideably located within the spindle forward of the ram which transfers the forward impacts from the ram to the tool or bit, for limited reciprocation within the tool holder at the front of the hammer. The mode change mechanisms for such hammers can selectively engage and disengage the rotary drive to the spindle and the reciprocating drive to the piston.
In a known type of mode change mechanism, a single mode change actuator is used to switch the hammer between different modes. However, mechanisms of this type tend to be relatively complex, use parts which are intricate and/or difficult to manufacture inexpensively in bulk, with sturdy qualities that can withstand sustained use of the hammer, and/or are relatively difficult to assemble.
A known mode change arrangement is disclosed in U.S. Pat. No. 5,159,986, and includes a mode change knob having a first cam element for activating and de-activating hammering, and a second cam for activating and deactivating rotary drive. The disclosed arrangement also includes the option of operating at either of two drive speeds. In a first position of the first cam element, rearward movement of the spindle is blocked, which prevents the drive from being transmitted to the hammer drive arrangement. In a second position of the first cam, rearward movement of the spindle occurs when the tool or bit is pressed against a work surface. This rearward movement of the spindle results in the engagement of two coupling parts which allows the drive to be transmitted from an intermediate shaft to the hammer drive arrangement.
The second cam arrangement, as described in U.S. Pat. No. 5,159,986, is used to guide an adjustment element along a rod mounted in the housing of the hammer, which adjustment element engages spindle drive gears to shift the gears between three positions. In a first of the three positions, a drive gear engages a spindle lock to prevent rotation of the spindle, and relates to of a surface of the first cam whereby drive is transmitted to the hammer drive arrangement. In a second position, a first drive gear engages the intermediate shaft to drive the spindle at a first speed of rotation, and, in a third position, a second drive gear engages the intermediate shaft to drive the spindle at a second speed. The three positions of the drive gears, as they relate to the orientation of the second cam element, are co-ordinated with the blocking and non-blocking positions, in relation to the orientation of the first cam element, in order to co-ordinate the activation of the spindle at the required speed with the activation of hammering.
The mode change arrangement as disclosed in U.S. Pat. No. 5,159,986 requires many non-standard type parts such as the first and second cam surfaces, an adjustment element, a bearing and a cage, which have to interact to change between the modes of operation. Such parts are relatively expensive to manufacture in such a way that the parts can survive sustained use of the hammer and still provide smooth changes between the different modes of operation of the hammer. Also, the assembling of the parts to provide such a mode change arrangement is relatively difficult, which further adds to the cost of manufacturing such hammers. Further, a biasing means between the knob and the adjustment element is required to bias the gears or teeth into position for meshing until one of the gears has rotated sufficiently to allow actual meshing to occur. This results in additional cost and complexity.